1. Field of the Invention
The present invention relates to a piezoelectric actuator, a method for manufacturing piezoelectric actuator, and a liquid transporting apparatus which includes the piezoelectric actuator.
2. Description of the Related Art
A piezoelectric actuator which drives an object by using a deformation developed in a piezoelectric layer when an electric field is made to act in the piezoelectric actuator has been hitherto used widely in various fields. For example, an ink-jet head, which discharges ink when a pressure is applied to the ink in a pressure chamber by the piezoelectric actuator, is described in U.S. Patent Application Publication No. US 2003/112298 A1 (corresponding to Japanese Patent Application Laid-open No. 2003-69103). This ink-jet head includes a metallic substrate, a plurality of piezoelectric elements (piezoelectric layer) arranged in the form of a matrix on the substrate, a piezoelectric actuator which has common electrodes and signal electrodes (individual electrodes) formed on an upper surface and a lower surface of the piezoelectric elements respectively, and a flexible printed circuit board (FPC) made of a resin base material.
A plurality of terminal sections is formed on the FPC on a surface facing the piezoelectric elements, and these terminal sections correspond to the signal electrodes on the upper surface of the piezoelectric elements. Each of the terminal sections has a hemispherical bump which includes a core material and a joining material. After positioning the signal electrodes and the bumps, the signal electrodes on the upper surface of the piezoelectric layer and the terminal sections of the FPC are electrically connected through the bumps by heating and pressurizing the FPC, or by applying vibration to the FPC from the surface of the FPC on the side opposite to the piezoelectric layer.
However, while joining the signal electrodes on the upper surface of the piezoelectric elements and the terminal sections of the FPC, stress acts locally in an area of each of the piezoelectric elements facing the bumps. Therefore, there is a possibility that the piezoelectric layer is damaged in the area. Moreover, in many cases, height of the bumps formed on the FPC is uneven. In this case, due to the uneven height, while connecting the electrodes on the upper surface of the piezoelectric layer and the terminal sections of the FPC, there is a portion where the electrodes on the upper surface of the piezoelectric layer and the bumps provided to the terminal sections of the FPC do not sufficiently contact with each other. Accordingly, there is a possibility of a poor connection between the electrodes on the upper surface of the piezoelectric layer and the terminals of the FPC.